Ponzo Optical Illusion

From Wikipedia, the free encyclopedia - The Ponzo illusion is an optical illusion that was first demonstrated by the Italian psychologist Mario Ponzo (1882-1960) in 1913. He suggested that the human mind judges an object's size based on its background. He showed this by drawing two identical lines across a pair of converging lines, similar to railway tracks. The upper line looks longer because we interpret the converging sides according to linear perspective as parallel lines receding into the distance. In this context, we interpret the upper line as though it were farther away, so we see it as longer – a farther object would have to be longer than a nearer one for both to produce retinal images of the same size.

I had been waiting quite a while for a great image to provide the backdrop for this illusion. Railroad tracks and long stretches of highway had been used to death. When I saw this great photo by Nuno Leitao I realized the search was over.

The two red lines (or three if you move your mouse over the image) below are duplicates, they are the exact same size. Which image is more convincing the one with two lines or the one with three lines?

Ponzo Illusion
(c) 2012 Walt Anthony

Original Photo:
(c) 2012 Nuno Leitao, used w/permission

Tags: photos, optical_illusions, illusions, art